DIXC hLE O..

1990 Thesis/i "

EMG Activity of Selected Trunk and Hip Muscles During aSquat Lift: Effect of Varying the Lumbar Posture

NJim Vakos

AFIT Student at: University of Kentucky~AFIT/CI/CIA -90-111

N

AFIT/CIS Wright-Patterson AFB OH 45433

Approved for Public Release IAW AFR 190-1Distribution UnlimitedERNEST A. HAYGOOD, Ist Lt, USAFExecutive Officer, Civilian Institution Programs

DTIC

115

UNCLASSIFIED

FOGG Act--lwity 4cx Sftxmc~td Twzxzuk MIM

Hjip rtxhamcl.w Otaxiza m S Qtamr LLft

Jim VakoxUniversity of Kentucky

Dept. of HPCR1990

90 1022 101

THESIS

Acoession Yor

NTIS GRA&IDTIC TABUnannounced 0

Justificato 1

James P. Vakos Distribution/Availability CodesI Avail and/or

Dist Special

The Graduate School

University of Kentucky

1990

01-1'

ABSTRACT OF THESIS

EMG ACTIVITY OF SELECTED TRUNK AND HIP MUSCLES DURING A SQUAT

LIFT: EFFECT OF VARYING THE LUMBAR POSTURE

- The electromyographic (EMG) activity of selected hip andtrunk muscles was recorded during a squat lift and the effectsof two different lumbar spine postures were examined. Sevenmuscles were analyzed: rectus abdominis (RA), abdominaloblique (AO), erector spinae (ES), latissimus dorsi (LD),gluteus maximus (GM), biceps femoris (BF), and semitendinosus(ST). The muscles were chosen because of their attachment tothe thoracolumbar fascia and their potential to act on themovement of the trunk pelvis and hips. Seventeen healthy malesubjects participated in this study. Each subject performedthree squat lifts with the lumbar spine in both a lordoticposture and a kyphotic posture. The lift was divided intofour equal time phases. EMG activity of each muscle wasquantified for each quarter of the lift and normalized to thepeak amplitude of a maximal isometric contraction and to thepeak amplitude recorded during the activity. A two-wayanalysis of variance for repeated measures was used to analyzethe effects of posture on the amount and timing of EMGactivity during the lift. --TWo different patterns of EMGactivity were observed in.this study: a trunk muscle pattern(RA, AO, ES, and LD) and a hip extensor muscle pattern (GM, \BF, ST). In the trunk muscle pattern, EMG activity was at a/maximum in the first quarter and decreased throughout the '-

remainder of the lift. In the hip extensor muscle pattern theEMG activity was at its minimum level in the first quarter,increased in the second and third quarters before plateauingor decreasing in the fourth quarter. Differences (p<.05) wereseen between subjects and between phases of the lift in allmuscles. A comparison of the two lumbar postures revealeddifferences (p<.05) in ES EMG activity in quarters one, three,and four, and in the ST muscle EMG activity in quarter four.The increased EMG activity seen in the lordotic lift in thefirst quarter indicates the ES muscle is involved to a greaterextent in the support of the lumbar spine. The greater ES EMGactivity seen in the third and fourth quarters in the kyphoticlift and the greater ST EMG activity observed during thefourth quarter in the lordotic lift appears to be the muscleaction required for the final reestablishment of the uprightposture.

(Author's Name)

(Dat e)

.. . .

MASTER'S THESIS RELEASE

I authorize the University of KentuckyLibraries to reproduce this thesis inwhole or in part for purposes ofresearch.

I do not authorize the University ofKentucky Libraries to reproduce thisthesis in whole or in part for purposesof research.

signed: 9Date: 9i 9o

RULES FOR THE USE OF THESES

Unpublished theses submitted for the Master's andDoctor's degrees and deposited in the University of Kentuckylibrary are as a rule open for inspection, but are to be usedonly with due regard to the rights of the authors.Bibliographical references may be noted, but quotations orsummaries or parts may be published only with the permissionof the author, and with the usual scholarly acknowledgements.

Extensive copying of publication of theses in whole orin part requires also the consent of the Dean of The GraduateSchool of the University of Kentucky.

A library which borrows this thesis for use by itspatrons is expected to secure the signature of each user.

Name and Address Date

EMG ACTIVITY OF SELECTED TRUNK AND HIP MUSCLES DURING A SQUAT

LIFT: EFFECT OF VARYING THE LUMBAR POSTURE

By

James P. Vakos

Directox of hesis)

(Director 6ftradue Studies)

(Date)

EMG ACTIVITY OF SELECTED TRUNK AND HIP MUSCLES DURING A SQUAT

LIFT: EFFECT OF VARYING THE LUMBAR POSTURE

THESIS

A thesis submitted in partial fulfillment of therequirements for the degree of Master of Science

at the University of Kentucky

By

James P. Vakos

Lexington, Kentucky

Director: Arthur J. Nitz

Associate Professor of Physical Therapy

Lexington, Kentucky

1990

ACKNOWLEDGEMENT

Thanks Dr. Arthur Nitz for your encouragement, support

and editorial assistance. I also thank Dr. Robert Shapiro and

Dr. Joseph Threlkeld for their help with the design of this

study and their technical support. Special thanks to Dr.

Kryscio for his statistical advice and to Terry Horn for his

help in computer programming.

iii

TABLE OF CONTENTS

ACKNOWLEDGEMENT.................... . . . .. .. .. . ...

LIST OF TABLES................................vi

LIST OFFIGURES................................vii

CHAPTER 1.... .. ......................... 1Statement of the Problem......................3Scope of the Study .................. 4

Limitations....................4Delimitations .................. 4Variables.....................4Assumptions....................5

Significance of the Study...............5

CHAPTER 2..........................7Support Mechanisms .................. 7

Intra-abdominal Pressure.............8Posterior Ligamentous System..........11

Stoop Lift vs. Squat Lift...............17Kyphosis.....................18Lordosis...................................20

Summary of Literature Review. ............ 20

CHAPTER 3.........................23The Subjects......................23

The Selection of Subjects...................23Description of Methods of Data Collection .. oo 24

Instrumentation.................24Electromyography.o................24Lifting Apparatus .............. 24Video Analysis System...........24

Procedure ..................... 25Electromyography. ............. 25EMG analysis..................29Video Analysis................30

Data Reduction and Analysis .............. 37Statistics.....................37

CHAPTER 4...........................39overview................. ........ 39Results........................54

Rectus Abdominal Muscles..............54Abdominal Oblique Muscles........ ..... 59Erector Spinae Muscles.o................64Latissimus Dorsi Muscle. ............ 70Gluteus Maximus Muscle ............... 75Biceps Femoris.................80Semitendinosus.................83

iv

Discussion ........ .................... 91

CHAPTER 5 .......... ....................... 99Summary ......... ..................... 99Conclusions .i.................. 100Recommendations for future study ........... . 102

APPENDIX A ......... ...................... 103Consent for Research Study ... ............ 104

APPENDIX B .. .............. ............ .... 108Medical History Questionnaire .. . ......... 109

BIBLIOGRAPHY ........... ..................... 110

VITA ........... ......................... 115

v

LIST OF TABLES

Table Pa~e

1. ANOVA Table - Rectus Abdominis (%MVIC).........40

2. ANOVA Table - Rectus Abdominis (%MDA) ........ 41

3. ANOVA Table - Abdominal Obliques (%MVIC) . ... 42

4. ANOVA Table - Abdominal Obliques (%MDA)........43

5. AN0VA Table - Erector Spinae (%MVIC). ....... 44

6. ANOVA Table - Erector Spinae (%MDA) .. ....... 45

7. ANOVA Table - Latissimus Dorsi (%MVIC)........46

8. ANOVA Table - Latissimus Dorsi (%MDA) .......... 47

9. ANOVA Table - Gluteus Maximus (%MVIC) .......... 48

10. ANOVA Table - Gluteus Maximus (%MDA). ....... 49

11. ANOVA Table - Biceps Femoris (%MVIC). ....... 50

12. ANOVA Table - Biceps Femoris (%MDA) .. ....... 51

13. ANOVA Table - Semitendinosus (%MVIC). ....... 52

14. ANOVA Table - Semitendinosus (%MDA) .. ....... 53

15. EMG Activity (%MVIC) - Rectus Abdominis .. ..... 55

16. EMG Activity (%MDA) - Rectus Abdominis. ...... 57

17. EMG Activity (%MVIC) - Abdominal Obliques . ... 60

18. EMG Activity (% MDA) - Abdominal Obliques . ... 62

19. EMG Activity (%MVIC) - Erector Spinae .. ...... 65

20. ENG Activity (%MDA) - Erector Spinae. ....... 68

21. EMG Activity (% VIC) - Latissimus Dorsi .. ..... 71

22. EMG Activity (%MDA) - Latissimus Dorsi. ...... 73

23. EMG Activity (% VIC) - Gluteus Maximus. ...... 76

vi

24. EMG Activity (%MDA) - Gluteus Maximus .. ...... 78

25. ENG Activity (%MVIC) - Biceps Femoris .. ...... 81

26. ENG Activity (%MDA) - Biceps Femoris. ....... 84

27. EMG Activity (%MVIC) - Semitendinosus .. ...... 86

28. ENG Activity (%MDA) - Semitendinosus. ....... 89

vii

LIST OF FIGURES

Figure Pacfe

1. The thoracolumbar fascia .... ............ .. 13

2. Placement of EMG electrodes .. ........... . 27

3. Plot of the EMG activity (% MVIC) recorded duringa squat lift with the lumbar spine in lordosis . . 31

4. Plot of the EMG activity (% MVIC) recorded duringa squat lift with the lumbar spine in kyphosis . . 32

5. Plot of the EMG activity (% MDA) recorded during asquat lift with the lumbar spine in lordosis . . . 33

6. Plot of the EMG activity (% MDA) recorded during asquat lift with the lumbar spine in kyphosis . . 34

7. EMG Activity (% MVIC) Rectus Abdominis ....... .. 56

8. EMG Activity (% MDA) Abdominal Obliques . ... 58

9. EMG Activity (% MVIC) Abdominal Obliques ..... . 61

10. EMG Activity (% MDA) Abdominal Obliques ..... 63

11. EMG Activity (% MVIC) - Erector Spinae ...... .. 66

12. EMG Activity (% MDA) - Erector Spinae ...... .. 69

13. EMG Activity (% MVIC) - Latissimus Dorsi ..... . 72

14. EMG Activity (% MDA) - Latissimus Dorsi ..... . 74

15. EMG Activity (% MVIC) - Gluteus Maximus ..... 77

16. EMG Activity (% MDA) - Gluteus Maximus ....... . 79

17. EMG Activity (% MVIC) - Biceps Femoris ....... .. 82

18. EMG Activity (% MDA) - Biceps Femoris ...... . 85

19. EMG Activity (% MVIC) - Semitendinosus ....... .. 87

20. EMG Activity (% MDA) - Semitendinosus ...... . 90

viii

CHAPTER 1

INTRODUCTION AND STATEMENT OF THE PROBLEM

Low back pain is one of the most common medical problems

seen in the United States, affecting 85% of all persons at

some time during their lives (Bigos, 1986; Spengler, 1986).

People are most commonly afflicted in their most productive

years, between the ages of 25 and 60 (Bigos, 1986) making low

back pain the most expensive medical condition for people in

the 30-50 age group (Spengler, 1986). Overall, it is the

third leading cause of disability in the United States and for

people under age 45 it is the most common. (Bigos, 1986;

Sullivan, 1989). In 1976 it was estimated that in excess of

$14 billion was expended on the treatment of low back pain and

for compensation secondary to disability caused by low back

pain (Spengler, 1986). One-fourth of all compensation for

industrial injuries is from low back pain (Bigos, 1986;

Delitto, 1987; Gagnon, 1985; McGill, 1985; Spengler, 1986;

Sullivan, 1989). Bigos (1986) in a survey of the airline

manufacturing industry found improper lifting and materials

handling to be the most commonly cited causes of back

injuries. Although lifting is a common activity in many

occupations and has been studied extensively, the support

mechanisms and forces sustained by the body are still not

fully understood (Delitto, 1987; Sullivan, 1989).

1

2

Lifts are usually categorized into two main styles; squat

and stoop (Andersson, 1976, 1977; Sullivan, 1989; Troup,

1977). A squat lift is performed by bending at the hips and

knees, so that the body is lowered down to the object to be

lifted. The stoop lift is executed by bending at the waist

with the knees kept relatively straight. During a squat lift

an individual's lumbar spine can assume a lordotic, (back

bowed in), or a kyphotic, (back bowed out) posture. The stoop

lift always has a kyphotic posture (Delitto, 1987; Hart,

1986). Lifting with the lumbar spine in a lordotic posture

is believed to decrease the strain on the ligamentous system

(Delitto, 1987; Hart, 1986), while lifting in a kyphotic

posture is hypothesized to decrease the compressive force on

the spine (Gracovetsky, 1985, 1981).

Lifting has been studied extensively by a number of

researchers (Andersson, 1977, 1976; Delitto, 1987; Ekholm,

1982; Hart, 1986; Hemborg, 1983; Kipper 1984; McGill, 1987;

Sihvonen, 1988; Zetterberg, 1987). Analysis of the

electromyographic (EMG) signal of a muscle group during

lifting can provide insight into the force developed by that

muscle (Anderrson, 1977; Jonsson, 1985). Myoelectric activity

of a muscle has been found to vary linearly with the tension

developed, in similar activities and non-fatigue situations

(Andersson, 1977; Jonsson, 1985). An increase in the level

AP

3

of EMG activity indicates an increase in force production by

the muscle, but the precise magnitude of the force is unknown.

Most electromyographic studies of lifting have been

focused on trunk muscle activity, rectus abdominis muscle,

external oblique abdominal muscle, erector spinae muscles,

and latissimus dorsi muscle, when lifting in different

postures (Andersson, 1977, 1976; Delitto, 1987; Ekholm, 1982;

Hart, 1986; Hemborg, 1983; Kipper, 1984; McGill, 1987;

Sihvonen, 1988; Zetterberg, 1987). An overlooked muscle

group that is anatomically positioned to assist in lifting is

the hip extensors: gluteus maximus muscles, gluteus medius

muscles, and the hamstring muscles (Gracovetsky, 1988). By

virtue of their attachment to the thoracolumbar fascia, via

the iliac bone, the hip extensors have an indirect connection

to the spinous processes of the lumbar spine (Bogduk, 1984;

Macintosh, 1987). Accordingly, activation of the hip extensor

musculature could exert an influence on the lumbar spine.

Statement of the Problem

The problem is that although the hip extensor muscles

have been believed to contribute to extension of the lumbar

spine when performing a lift in a kyphotic posture, their

function has not been analyzed. The purpose of this study was

to determine the function of muscles anatomically related to

the thoracolumbar fascia and lumbar spine (with particular

emphasis on the hip extensor muscles) during a squat lift and

4

to see what effect, if any, changing the lumbar posture has

on that function. The research hypothesis was that squat

lifting with the lumbar spine in a kyphotic position would

result in a significant increase in the amount of myoelectric

activity seen in the hip extensor muscles when compared to

squat lifting with lumbar spine in a lordotic position.

Scope of the Study

Limitations

This study was limited by the following:

There was no control of the subjects activities,

prior to the data collection.

Use of surface EMG electrodes to collect the data.

Delimitations

The study was delimited by the following:

Subjects to be used are males between the ages of

19 and 40.

Subjects are in a good state of health, with no

recent history of low back pain with no recent

history of low back pain, or knee pathology

interfering with an ability to squat.

Variables

The independent variable was the style of lift. Each

subject performed three squat lifts, using two different

5

lumbar spine postures: 1) lumbar spine in kyphosis, and 2)

lumbar spine in lordosis. The dependent variable was the

amount of myoelectric activity recorded.

Assumptions

The following assumption were made:

That all subjects responded honestly on the

questionnaire about present state of health and

previous low back pain.

That a symmetrical lift produced equal EMG activity

bilaterally (Cook, 1987; Seroussi, 1987;

Sihvonen, 1988).

Significance of the Study

Low back pain is a common condition thought to affect up

to 80% of the adult population in Western Europe and the

United States (Andersson, 1981). Lifting is frequently cited

as a cause of low back pain in working populations (Bigos,

1986). Prior research on lifting techniques has primarily

centered on the role played by the trunk musculature

(Andersson, 1977, 1976; Delitto, 1987; Ekholm, 1982; Hemborg,

1983; McGill, 1987; Zetterberg, 1987). This study

investigates the function of the hip extensor musculature

during a squat lift and the effect that two variations in the

lumbar posture have on this function. This increased

knowledge of muscle activity during a lift may lead to a

6

greater understanding of the forces incurred by the lumbo-

sacral spine during a lift. It is hoped that safer techniques

of lifting may then be developed which will better protect the

worker and decrease the incidence of low back pain in the

work-place.

CHAPTER 2

LITERATURE REVIEW

In the United States and Western Europe low back pain has

been shown to be a leading cause of disability and lost time

at work especially in occupations involving manual labor

(Andersson, 1981). Because of the cost of these injuries in

medical expense and disability payments there has been a great

deal of interest and study of manual lifting (Andersson, 1985,

1977, 1976; Aspden, 1989; Bush-Joseph, 1988; Cook, 1987;

Delitto, 1987; Ekholm, 1982; Freivalds, 1984; Gagnon, 1985;

Gracovetsky, 1988, 1985, 1981; Hart, 1987; Hemborg, 1983;

Jonsson, 1985; Kippers, 1989; McGill, 1987, 1986, 1985;

Ortengren, 1981, Seroussi, 1987; Troup, 1977; Zetterberg,

1987). Despite this work there is a still disagreement over

their back support mechanism of proper lifting techniques and

the forces sustained by the lumbar spine while lifting. This

chapter will briefly review lumbar support mechanisms, anatomy

of the thoracolumbar fascia and squat lifting.

Support Mechanisms

Two postulated mechanisms for support of the lumbar spine

while lifting are intra-abdominal pressure, and the posterior

ligamentous system. Each system has it supporters and

7

detractors but neither theory has been fully validated

experimentally, nor has either been totally refuted.

Intra-abdominal Pressure

The intra-abdominal pressure mechanism of reducing

compressive forces on the spine during lifting was first

proposed by Bartelink in 1957. A rise in intra-abdominal

pressure as measured with a gastric balloon was noted when

subjects lifted. Andersson (1976) determined that the intra-

abdominal pressure increased as the load increased or as the

amount of forward bending of the trunk increased. The rise

in intra-abdominal pressure coincided with an increase in EMG

activity of the transversus abdominis and internal oblique

muscles. It was concluded that contraction of the abdominal

muscles in the presence of a closed glottis produced a rise

in the intra-abdominal pressure creating a "balloon" in front

of the vertebral column that resisted compression and gave an

anti-flexion moment to the lumbar spine (Bartelink, 1957,

Andersson, 1976). This anti-flexion moment assisted the

extensor muscles of the spine. Therefore, the extensor

muscles did not have to contract as hard and compression on

the spine secondary to erector spinae muscle contraction was

decreased.

9

The concept of intra-abdominal pressure decreasing

compression through creation of an anti-flexion moment is not

universally accepted. Objections have been raised on a

theoretical level. Calculations of the intra-abdominal force

needed to provide the necessary upward force on the thorax

exceed the systolic aortic blood pressure (Gracovetsky, 1985).

If these pressures were developed, they could only be

sustained for a short period of time to avoid compromising

lower extremity circulation. The calculated force of

contraction of the abdominal muscles necessary to generate

this tension exceeds the maximum tension the muscles could

produce (Gracovetsky, 1985). Additionally, any increase in

intra-abdominal pressure produced by abdominal muscle activity

would also produce a flexion moment of the trunk (Gracovetsky,

1985; McGill, 1987; and Macintosh, 1987). To offset the

increased flexion moment requires increased erector spinae

muscle activity, resulting in an increase in spinal

compression (Gracovetsky, 1985; McGill, 1987; and Macintosh,

1987). Aspden calculated that the intra-abdominal pressure

acting on the convex surface of a lordotic lumbar spine

results in an increase in discal pressure and increased

compression on the tissues of the lumbar spine (Aspden, 1989).

His calculations show that this compression results in

increased stability and is within safe limits for the tissues

of the lumbar spine (Aspden, 1989).

. . .. -. .. . .. .. .

10

Recent evidence has indicated that the role of intra-

abdominal pressure in decreasing compression on the lumbar

spine may be overrated (McGill, 1987, 1986; Nachemson, 1986).

McGill (1987) cited studies showing that laborers lifting

with increased intra-abdominal pressure had increased rates

of low back injury. If increased intra-abdominal pressure

actually protected the spine then subjects should have

exhibited decreased injury rates. Increased intra-abdominal

pressure, due to a valsalva maneuver, resulted in increased

disc compression, not decreased (Nachemson, 1986). Andersson

(1976) found that when people lifted and consciously tensed

their abdominal muscles, the compression on the spine did not

decrease. Hemborg (1982) found intra-abdominal pressure to

be load specific. Training of the abdominal musculature

resulted in increased abdominal muscle strength but not in

increased intra-abdominal pressure (Hemborg, 1982, Macintosh,

1987). McGill (1990) observed increased intra-abdominal

pressure during sit-ups while the lumbar spine was flexing.

However, according to proponents of the intra-abdominal

pressure theory, increase in intra-abdominal pressure was

thought to inhibit flexion of the lumbar spine during lifting.

Posterior LiQamentous System

The role of the posterior ligamentous system and

thoracolumbar fascia in the support of the lumbar spine has

received substantial attention (Bogduk, 1984; Gracovetsky,

1981, Macintosh, 1987). This theory called for the

transmission of the power of the hip extensor muscles through

the lumbar spine to the trunk and eventually to the arms by

way of the posterior ligamentous system and thoracolumbar

fascia (Gracovetsky, 1988; Bogduk, 1987). A brief review of

the anatomy of the thoracolumbar fascia will assist in the

understanding of these functions.

The thoracolumbar fascia is comprised of three layers,

anterior, middle and posterior (fig. 1) (Macintosh, 1987).

These layers envelop the muscles of the lumbar spine and

separate them into three compartments (Bogduk, 1987). The

anterior layer of thoracolumbar fascia arises from the

anterior surface of the lumbar transverse processes, covers

the anterior surface of the quadratus lumborum and attaches

laterally at the lateral raphe with the other layers of the

thoracolumbar fascia (Bogduk, 1984; 1987; Macintosh, 1987)

The middle layer of thoracolumbar fascia arises from tips

of the lumbar transverse processes and lies posterior to the

quadratus lumborum (Bogduk, 1984; 1987; Macintosh, 1987).

12

Laterally, the transversus abdominis takes its origin from

middle layer.

The posterior layer of thoracolumbar fascia arises from

lumbar spinous processes and covers the erector spinae muscles

(Bogduk, 1984; Macintosh, 1987). It attaches laterally,

blending with the other layers of the thoracolumbar fascia,

along the lateral border of the iliocostalis lumborum and

forms a dense raphe (Bogduk 1984; 1987). This has been termed

the 'lateral raphe' (Bogduk, 1984). The thoracolumbar fascia

has a cross-hatched appearance because it consists of two

laminae, superficial and deep, which are fused together and

form a network of obliquely crossing fibers extending from the

lateral raphe to the midline (Bogduk, 1984). The superficial

lamina has fibers orientated caudomedially and the deep lamina

has fibers oriented caudolaterally (Bogduk,1984; Macintosh,

1987).

The superficia3 lamina fibers provide the latissimus

dorsi with an attachment to the spinous processes of the

vertebral column (Bogduk, 1984). Contraction of the latissimus

dorsi exerts an upward and lateral force on the upper lumbar

vertebrae (Bogduk, 1984). On the lower lumbar vertebrae the

force is lessened because the aponeurosis of the latissimus

dorsi is fused with the lateral raphe (Bogduk, 1984). This

spreads the force through the lateral raphe to the iliac

crest (Bogduk, 1984).

13

PosteriorLayerMiddlLayer

Reflected" ,._ Postrerior

Layer

Figure 1. The thoracolumbar fascia. The posterior layer iscomprised of separate laminae running in different directions,giving a crosshatched appearance. (Reprinted from Spine, 2i,pg. 502).

14

The deep lamina of the posterior layer serve as

retinacular fibers and as accessory ligaments (Bogduk, 1984).

The fibers from the L2-L3 spinous processes fuse with the

middle layer of the thoracolumbar fascia forms a retinaculum

surrounding the erector spinae muscles (Bogduk, 1984). The

fibers from the spinous processes of L4-L5 connect to the iliac

crest, forming a retinaculum over the multifidus and the lower

portion of the longissimus thoracis (Bogduk, 1984). The

fibers from L4-L5 because of their bony attachments can also

serve as accessory ligaments (Bogduk, 1984).

The superficial and deep laminae from the posterior layer

join together at the lateral raphe along with middle layer of

the thoracolumbar fascia and the transversus abdominis, whose

fibers arise from the middle layer (Bogduk, 1987). This

provides the transversus abdominis with an indirect connection

the lumbar spinous processes through the posterior layer of

the thoracolumbar fascia (Bogduk, 1987).

The posterior ligamentous mechanism can act either

passively or actively (Gracovetsky 1985; 1981). It acts

passively when the spine is flexed and the ligaments are taut.

Extension of the hip causes posterior rotation of the pelvis

(Gracovetsky, 1988; Bogduk, 1987). The posterior rotation of

the pelvis is transmitted to the lumbar spine through the

lumbosacral joints, the L5-S, interspinous ligament, the ilio-

15

lumbar ligaments, and the thoracolumbar fascia (Bogduk, 1987).

It is succeedingly transmitted up the spine to the thorax via

the posterior elements and rotates the thorax posteriorly

producing a lift (Bogduk, 1987). This passive mechanism is

possible only as long as the lumbar spine is in a flexed

position and the ligaments are taut (Bogduk, 1987). When the

spine extends, the ligaments relax and can no longer transmit

forces to the thorax (Bogduk, 1987). This drawback is

compensated by another mechanism that acts independently of

spinal flexion angle and operates in concert with the

posterior ligaments (Bogduk, 1987; Gracovetsky, 1985; 1981).

The posterior layer of the thoracolumbar fascia provides the

basis of this mechanism (Bogduk, 1987). Because of the

thoracolumbar fascia's muscle attachments and its role as a

ligament the fascia is thought to be a major support mechanism

for lifting regardless of the lumbar posture adopted (Delitto,

1987; Gracovetsky, 1981; McGill, 1985). There are thought

to be three methods by which the posterior layer of the

thoracolumbar fascia can stabilize the lumbar spine and assist

in lifting (Bogduk, 1987; 1984). The first function is the

aforementioned passive ligamentous role of the deep lamina

(Bodguk, 1987). The deep lamina provides a direct connection

of the L4 - L spinous processes to the ilium. The ligaments

are tense when the lumbar spine is flexed (Bogduk, 1987). A

second function of the thoracolumbar fascia is derived from

the crosshatching fibers of the two lamina and the attachments

16

of the lateral raphe and transversus abdominis (Bogduk, 1987).

The divergent direction of the fibers produces a pattern of

overlapping triangles with apex in the lateral raphe and base

spanning two vertebral levels in the midline (Bogduk, 1984).

A lateral tension applied to a given point of the lateral

raphe will spread out over a triangular area and produce an

extension moment at the midline (Bogduk, 1984; 1987).

Contraction of the transversus abdominis acting through its

attachment at the lateral raphe can produce an anti-flexion

moment of the lumbar spine (Bogduk, 1987). The third function

of the thoracolumbar fascia arises from the of the posterior

layer's retinacular structure (Bogduk, 1987). This layer is

relatively indistensible and resists expansion of the lumbar

muscles as they contract (Bogduk, 1987; Gracovetsky, 1977).

An increased tension in the fascia's posterior layer will

result, augmenting the anti-flexion properties of the

thoracolumbar fascia (Bogduk, 1987). This has been termed the

'hydraulic amplifier mechanism' (Gracovetsky, 1987).

The chief advantage cited for the posterior ligamentous

theory is that the thoracolumbar fascia has the greatest

mechanical advantage of all the tissues of the lumbar spine

that provide an anti-flexion moment (Sullivan, 1989). Because

of this the thoracolumbar fascia produces the least amount of

compressive force on the lumbar spine (Gracovetsky, 1985).

17

Recent research has identified problems with the

thoracolumbar fascial model of the lumbar spine (Bogduk, 1984;

Macintosh, 1987; McGill, 1987). The thoracolumbar fascia,

though anatomically capable of transforming the lateral pull

of the abdominal muscles into an extensor moment on the lumbar

spine, does not possess muscle fibers of sufficient number or

suitably arranged mass to exert a significant anti-flexion

moment (Bogduk, 1984; McGill, 1987; 1986; Macintosh, 1987).

Stoop Lift vs. Squat Lift

In addition to examining the support mechanisms of the

lumbar spine investigators have been studying the most

efficient and safest method of lifting (Andersson, 1977, 1976;

Delitto, 1987; Ekholm, 1982; Hart, 1986; McGill, 1987, 1986,

1985; Ortengren, 1981; Seroussi, 1987; Troup, 1977). The

squat lift is considered to be a much safer lift than the

stoop lift for the following reasons: 1) the center of

gravity of the load is held closer to the body decreasing the

spinal flexion moment, 2) early onset of the erector spinae

muscle activity protects the inert structures, 3) leg muscles

are more active to assist in the lift, and 4) horizontal

movement of the weight can be initiated by the body (Delitto,

1987). The squat lift can be performed with the lumbar spine

in either a kyphotic or lordotic posture. Advocates exist for

18

both postures (Gracovetsky, 1981; Sullivan, 1989). The

advantages of the stoop lift are: 1) it requires less energy

expenditure than the squat lift, 2) it decreases compression

on the lumbar spine (Gracovetsky, 1981; Sullivan, 1989).

Kyphosis

Advocates of lifting with the lumbar spine in a kyphotic

position believe it is a more efficient system and decreases

compression on the lumbar spine (Gracovetsky, 1988, 1985,

1981). Less electrical activity is recorded from the erector

spinae musculature when lifting with the lumbar spine in a

kyphosis (Delitto, 1987; Hart 1986). This is especially true

at the start of the lift where little or no activity is seen

in the erector spinae musculature (Andersson, 1977, 1976;

Kippers, 1984). The decreased activity means that inert

structures are used almost exclusively early in the lift and

it is not until the later stages that the muscles take over

and complete the lift (Hart, 1986). One explanation for the

decreased activity of the erector spinae is that the kyphosis

puts the erector spinae in a more lengthened and efficient

position which decreases the need for high levels of activity

(Sullivan, 1989). The decreased activity results in decreased

compression on the posterior elements of the spine (cited by

Delitto, 1987). Lifting with a kyphosis utilizes ligaments

possessing longer moment arms than the muscles (Gracovetsky,

1988, 1985, 1981). The increased efficiency results in a

19

decrease in compression on the spine (Gracovetsky, 1988, 1985,

1981).

When lifting with the lumbar spine in kyphosis the

extension of the spine is thought to be accomplished by muscle

action through the use of the thoracolumbar fascia mechanism

(Gracovetsky, 1988, 1985, 1981) The thoracolumbar fascia by

nature of its attachment to the spinous processes, lateral

raphe, latissimus dorsi and iliac bone is ideally positioned

to extend the spine from the flexed position (Bogduk, 1987,

1984; Gracovetsky, 1988, 1985, 1981). However, the angle of

insertion of the latissimus dorsi and abdominal muscles onto

the thoracolumbar fascia the activity and mass of these

muscles is not great enough to provide a sufficient extension

moment to the lumbar spine (Bogduk, 1984; McGill, 1987, 1986;

Macintosh, 1987). The hip extensor muscles are also

anatomically positioned to extend the trunk. The gluteus

maximus, and hamstrings along with the erector spinae muscles

are the prime mover muscles in trunk flexion and extension in

an upright subject (Carlsoo, 1961; Gracovetsky, 1988; Tanii,

1985). During forward flexion of the trunk the hamstring

muscles display myo-electric activity throughout the range of

motion. The gluteus maximus becomes active near the angle of

maximum trunk flexion (Carlsoo, 1961; Portnoy, 1958; Tanii,

1985). Extension from the fully flexed position finds myo-

electric activity in both the hamstrings and gluteus maximus

20

(Carlsoo, 1961; Portnoy, 1958). Thus, the hamstrings are

active throughout trunk flexion/extension with the gluteus

maximus active when more power is required (Joseph, 1958).

Lordosis

Proponents of lifting with the lumbar spine in a lordotic

position contend a decreased stress is placed on the posterior

elements of the lumbar spine (Hart, 1986). Others contend

that there is actually increased compression (Andersson, 1976;

Aspden, 1989; Gracovetsky, 1988, 1985, 1981). Aspden (1989)

reports that along with increased erector spinae muscle

activity there is increased compression but, the compression

is well within the tissues ability to withstand. This

increased erector spinae activity along with increased intra-

abdominal pressure recorded when lifting with the lumbar spine

in a lordosis, prestresses the spinal tissue giving increased

stability to the spine and protection to the inert ligamentous

structures. (Aspden, 1989; Delitto, 1987; Hart, 1986).

Summary of Literature Review

Regardless of style of lifting technique advocated,

researchers agree that the erector spinae muscles are much

more active when the spine is in a lordotic position (Delitto,

1987; Hart 1986). With increasing trunk flexion angle the

electrical activity of the erector spinae decreases until a

21

position of electrical silence is reached when the spine is

in about 90% of maximal trunk flexion. Because of the

muscular silence the weight of the trunk is borne passively

on the posterior ligamentous system (Kipper, 1984). When

extending from a flexed position, it is not until late in the

motion that the erector spinae EMG activity increases back to

the EMG activity level present early in a lordotic position

(Hart 1986; Kipper, 1984).

Early extension of the spine from the fully flexed

position is thought to be accomplished by muscle contraction

through the use of the posterior ligamentous system

(Gracovetsky, 1988, 1985, 1981). It is still not entirely

certain which muscles are controlling this mechanism. Some

believe that the abdominal muscles and the latissimus dorsi

are the muscles responsible (Gracovetsky, 1988, 1985, 1981).

However, the myo-electric activity seen in the abdominals and

latissimus dorsi does not imply sufficient strength to extend

the spine given their attachments (McGill 1987, 1986;

Macintosh, 1987). The hip extensor muscles are also

anatomically positioned to move the trunk by acting through

the ilium, an indirect connection to the thoracolumbar fascia.

Posture of the lumbar spine exerts an influence over the

electrical activity of the erector spinae muscles when using

a squat lift (Delitto, 1987; Hart, 1986). Greater myo-

22

electrical activity is seen in the erector spinae muscles when

the lumbar spine is in a lordotic posture versus a kyphotic

posture (Delitto, 1987; Hart, 1986). Since the hip extensor

muscles can control trunk flexion and extension, they should

demonstrate increased electrical activity when lifting in a

kyphotic position, if the posterior ligamentous system is

involved.

CHAPTER 3

METHOD

This chapter will review the selection of the subjects,

the instrumentation used in this study, and the methodology

of data collection and analysis.

The Subjects

The Selection of Subjects

Seventeen healthy male subjects ranging in age from 20

to 38 years (X 26.94 years). Each subject answered a

questionnaire about present status of health and injury.

Subjects were excluded from the study for the following

reasons:

1) History of back pain or trauma to the low back within

the last six months.

2) Knee pithology interfering with an ability to squat.

3) Cardiac precautions.

4) Respiratory problems preventing exertion.

The experimental procedure was explained to each subject

and all questions about the research were answered. Subjects

then read and signed a consent form approved by the University

of Kentucky's Human Studies Committee.

23

24

Description of Methods of Data Collection

Instrumentation

Electromyography. Bipolar silver-silver chloride surface

electrodes i, (.05cm in diameter, 2 cm apart), and on-site

preamplifiers were used in this study. Electromyographic

signals were amplified2 and recorded by a micro-computer after

analog to digital conversion3 , at a sampling rate of 1000 Hz.

Lifting Apparatus. The subjects lifted a plastic crate

(28 cm high, 33 cm deep and 33 cm wide), weighing 157 N. The

weight selected was in accordance with safe and acceptable

limits set by the Industrial Labor Organization The lifting

crate had holes for hand holds 25 cm above the floor allowing

for consistent hand placement. Two reflective markers, (one

on each side), were placed on the sides of the crate so that

the movement could be followed throughout the lift.

Video Analysis System. A quantitative analysis of the

lift was performed by high speed videography. The "Expert-

I Therapeutics Unlimited; D-100 preamplified electrodes;

2835 Friendship St; Iowa City, IA 52240

2 Ibid. Model # EMG-67 EMG Amplifier Processor

3 Data Translation, Inc.; Model # DT-2821-F-16SE; 100Locke Dr.; Marlboro, MA 01752

25

Vision" system (Motion Analysis Corporation4) was used to

extract kinematic data from raw video signals. The subjects

were filmed by four phase-locked NAC5 high-speed video cameras

at 60 frames/second. The cameras run synchronously with the

EMG recorded from the subject during the lift. Two cameras

were placed in front of the subject, and two were placed

behind the subject. The cameras were placed to insure that

all reflective markers were in view of at least two cameras

at all times. The points on the lifting crate were

automatically identified by the Motion Analysis System and

computer digitized on a Sun Workstation6. This information

gave a mathematically generated three-dimensional record of

the movement of the lifting crate.

Procedure

Electromyography. The skin was wiped with alcohol before

application of the electromyographic electrodes. Only right

side musculature was monitored as other researchers have shown

that when lifting or carrying loads in the midline the myo-

electric signals are symmetrical bilaterally (Cook, 1987;

Motion Analysis Corporation; 93 Stony Circle; Sana Rosa,CA; Software v. 2.01

NAC Model #HVRB-2000; NAC Inc.; No. 2-7 Nishi-Azuba 1-chome; Minato-ku, Tokyo, Japan

Sun Microsystems; Model # Sparc Station 330; 2550 GarciaAve; Mountain View, CA 94043.

26

Seroussi, 1987; Sihvonen, 1988). All electrodes were applied

in line with the direction of the muscle fibers. The location

of the electrode were as follows (fig. 2):

1) Over the muscle belly of the erector spinae (ES)

muscles horizontally aligned with the

interspace, 4cm lateral to the midline.

2) Over the oblique abdominals (AO) muscles, posterior

to the midway point of a line running vertically

from the ASIS to the 1 2 th rib.

3) Over the rectus abdominis (RA) muscle, 2cm cranial

and 2cm lateral to the umbilicus.

4) Over the gluteus maximus (GM) muscle, at the midway

point on a line connecting the inferior lateral

angle of the sacrum and greater trochanter.

5) Over the latissimus dorsi (LD) muscle, 5cm inferior

and 3cm lateral to the infericr angle of the

scapula.

6) Over the biceps femoris (BF) muscle, at the junction

of its proximal two-third and distal one-third.

7) Over the semitendinosus (ST) muscle, midway between

its insertion on the upper part of the tibia and its

origin on the ischial tuberosity.

27

AbdominalObliques Ltsiu os

RectusAbdominus MErector Spinac

GluteusMaximus;

I Semitcndinosis

Biceps Femoris

Figure 2. Placement of EMG electrodes.

28

A quiet EMG reading was taken for each muscle and recorded,

then a maximal voluntary isometric contraction (MVIC) was

elicited and recorded. From a pilot project performed on

eight subjects the following positions were found to give the

greatest EMG signals for maximal contraction:

1) Rectus Abdominis (RA). The subjects were positioned

supine with hips and knees flexed 900 and lower leg

supported on a chair. The subjects crossed their

arms over their chest and attempted to flex their

trunk while manual resistance was applied at the

shoulders.

2) Abdominal Obliques (AO). Subjects lay supine with

their hips flexed 900 and knees straight. The

subjects attempted to rotate their lower trunk to

the right while the tester applied manual resistance

lateral side of the lower leg.

3) Erector Spinae (ES). The subjects lay prone with

their arms at their sides. The subjects then

arched their backs lifting their chest off of the

table while the tester applied manual resistance to

the back of the shoulders.

4) Latissimus Dorsi (LD). The subjects stood with their

right arm in slight flexion and abduction. The

P

29

subjects attempted to extend and adduct the arm

against maximal manual resistance.

5) Gluteus Maximus (GM). The subjects lay one-half way

between prone and left side-lying. The right leg

is brought into extension and abduction. The

subject resists against the tester trying to move

the leg into flexion and adduction.

6) Biceps Femoris (BF). Subject lies prone with right

knee flexed 900. The subject attempts to further

flex the knee against resistance applied by the

tester.

7) Semitendinosus (ST). Same as biceps femoris.

EMG analysis. All signals collected during the test

underwent an analog to digital conversion rz a frequency of

1000 hz. Based on the total time duration of the lift,

determined through video analysis, the lift was normalized to

a percentage of cycle and divided into four equal phases, each

consisting of 25% of the total cycle. A customized software

package7 was used to calculate the average peak intensity for

each muscle during each phase of the lift. Two methods were

used to normalize the EMG signals recorded in this study. The

EMG activity during the lift was expressed as: 1) as a

percentage of the maximum volitional isometric contraction

Asyst v. 2.1; Mcmillan Software Co.; 866 Third Ave.; NewYork, NY 10022

30

(figs. 3-4) (% MVIC) and 2) as a percentage of the maximum EMG

activity recorded during the activity (figs. 5-6) (% MDA).

The EMG activity values of three trials for the same condition

were averaged.

Video Analysis. Prior to data collection for each

subject the cameras and motion analysis system were calibrated

according to manufacturers instructions8 Reflective markers

were used to define a space four feet wide by four feet long

by eight feet high. All lifting was done within this defined

space. Reflective markers were placed on the sides of the

lifting crate and the reflective markers were tracked as they

moved through space while the subjects performed the lifts.

The computer assigned X and Y coordinates to the markers at

each point in time. When two cameras have a marker in view

the Z coordinates may be affixed to that marker. In this way

a mathematical 3-dimensional construction of path of the

markers can be constructed. The beginning and end points of

the lift were determined through video analysis. The start

of the lift was defined as the point where the vertical

movement and vertical velocity of the box first moved in a

positive direction. The end point of the lift was that point

where the box vertical height reached a maximum and the

velocity reached zero.

Motion Analysis Corporation; 93 Stony Circle; Sana Rosa,

Ca. software v. 2.01

31

EM; Ativity (Z WIC) Lordosis

Rectus Abdominus

100%Abdominal Obliques

0%

108Z

Latissimus Dorsi

Gluteus Maximsus

021002

atat

Vertca Height ................. PahVertical Velocityofithe BoxoftBx

0 O .... Wee

Percent of Lift Cycle

Figure 3. Plot of the EMG activity (% mvic) recorded duringa squat lift with the lumbar spine in lordosis.

32

EMG Activity (% IC) Kyphosis100%

Rectus Abdominus

100%Abdominal Obliques

OX

1000Erector Spinae

109ZLatissimus Dorsi

100%Gluteus Maximus

100Biceps Femoris

O .k,._1. L *,,U al- kd_.iL .IL.JJ, H J

1092

Semitendinosis

so050 isecVerticW Height - Path .. Velocity Vertical Velocityof the box ... .... ....... of the Box

o 25 50 75 100

Percent of Lift Cycle

Figure 4. Plot of the EMG activity (% MVIC) recorded duringa squat lift with the lumbar spine in kyphosis.

33

ENG Activity (% MWA Lordosis

1o~ ~jRjJceusUS bdominus

Iaon% Abdominal Obliques'

pina

1002

Vertical Hej.......... ... Pit . CIt VertcalVelocity~of the Box

o. M 1.111 5

Percent of Lift Cycle

Figure 5. Plot of the EMG activity (% MDA) recorded duringa squat lift with the lumbar spine in lordosis.

34

FEJG Activity (Z MM) XyphOSiS

IErector Sp .n

Figure 6 Plot of the E? G a tiv Sity (% WA r co dea s ua l ft wi h he lu bar Sp ne in ky ho is du in

35

Each subject performed both styles of lifts. The

procedure for each type of lift was explained to the subject

and the subjects were allowed to practice until the tester

felt the lift was being executed properly and the subjects

felt comfortable performing the lifts. A minimum of one

minute rest was given between the lifts during the practice

and testing sessions, to avoid fatigue. The order in which

the lifts were performed was selected randomly for each

subject. Subjects lifted at their preferred pace, completing

three repetitions for each type of lift. Amount of

lordosis/kyphosis at the start of the lift was determined

through the use of a flexible ruler9. The technique of Hart

and Rose modified such that L3 was used as the top point of

the curve instead of L, (Hart, 1986). The subject's lordosis

was measured in the standing position and again when the

subject assumed the squatting position, prior to lifting. For

the lordotic lift the subjects would 'arch their low back'

until the shape of the flexible ruler matched the shape

measured with the subject standing. For the kyphotic lift the

subject would 'flatten their low back' until the curve

measured was straight or nearly straight, ensuring less

lordosis in the starting position. The distance from the

floor to the greater trochanter was measured with a metal

ruler with the subject in a squat position to ensure

consistent hip and knee flexion angles at the start of the

9 The C-Thru Ruler Company; Bloomfield, CT, 06002

AP

36

lift. The subject would begin each lift with the greater

trochanter at the same height. All lifts were performed with

the arms straight or nearly straight.

37

Data Reduction and Analysis

The lift was divided into four equal phases based on the

total duration (as determined by video analysis). The EMG

activity of the ES, RA, AO, GM, BF, ST, and LD was quantified

by determining the average peak intensity during each phase

of the lift (analysis by custom computer software package) and

expressing this as a percentage of the peak intensity of a

maximal contraction (% MVIC) (figs. 1, 2) and as a percentage

of the maximum peak intensity occurring during the activity

(% MDA) (figs. 3, 4). Average maximum peak amplitudes of the

MVIC and MDA were calculated by a customized computer software

package. The digitized signal was rectified and sorted by

amplitude. The mean of the 50 highest amplitudes of the

isometric test contractions was used to compute the MVIC and

the mean of the 100 highest amplitudes of the actual lift was

used to determine the MDA.

Statistics

A two-way analysis of variance (2 x 4) for repeated

measures was performed to analyze the effect of the following

factors on the amount of EMG activity:

1) Factor I - Style of lift (lordosis vs.

kyphosis).

2) Factor II - Phase of the lift (first quarter

vs. quarters two, three and four, second

38

quarter vs. quarters three and four and third

quarter vs. fourth quarter).

Each muscle was analyzed separately. Results were

considered significant at the level of p < .05.

CHAPTER 4

RESULTS AND DISCUSSION

This chapter will present the results of the analysis and

discuss differences found in the two lifting styles. The

results of each method (% MVIC and % MDA) of analysis will be

treated separately

Overview

Generally, a comparison of the EMG activity (% MVIC and

% MDA) recorded in each phase of the lift and in each muscle

in both the lordotic and kyphotic styles found more

similarities than differences. All muscles tested showed

differences (p < .05) between subjects and between phases

within a lift (tabs. 1-14) except the BF muscle, and GM

muscle, where a difference (p<.05) was not seen between the

individual subjects, using % MDA analysis (tabs. 10, 12). A

difference (p<.05) was found between the lordotic and kyphotic

lifting styles (style) in only the erector spinae muscles,

with % MVIC analysis, (tab. 6). Differences (p<.05) in the

timing of EMG activity (phase vs style interaction) was found

in the erector spinae muscle, % MVIC and % MDA, and the

semitendinosus, % MDA (table 5,6 and 12). A more detailed

analysis of each muscle follows.

Ia

40

Table 1. ANOVA Table - Rectus Abdominis (%MVIC)

Source df ss ms if ratio

Subject 16 121.26 7.58 56.94*

Style 1 0.03 0.03 0.26

Phase 3 6.37 2.12 15.95*

Phase vs Style 3 0.17 0.06 0.43

Error 112 24.91 0.13

Total 135 142.74

*p < .05

41

Table 2. ANOVA Table - Rectus Abdominis (% MDA)

Source df ss ins f ratio

Subject 16 923.70 57.73 3.21*

Style 1 37.41 37.41 2.08

Phase 3 3107.50 1035.83 57.54*

Phase vs Style 3 35.65 11.88 0.66

Error 112 2016.38 18.00

Total 135 6120.63

*p< .05

42

Table 3. ANOVA Table - Abdominal Obliques (% MVIC)

Source df ss ms f ratio

Subject 16 202.51 12.66 52.01*

Style 1 0.12 0.12 0.47

*

Phase 3 13.43 4.48 18.39

Phase vs Style 3 0.13 0.04 0.18

Error 112 27.26 0.13 38.62

Total 135 243.44

* p < .05

43

Table 4. ANOVA Table - Abdominal Obliques (% MDA)

Source df ss ms f ratio

Subject 16 923.70 57.73 3.21*

Style 1 37.41 37.41 2.08

Phase 3 3107.50 1035.83 57.54

Phase vs Style 3 35.65 11.88 0.66

Error 112 2016.38 18.00

Total 135 6120.63

* p < .05

44

Table 5. ANOVA Table - Erector Spinae (% MVIC)

Source df ss ms f ratio

Subject 16 6978.78 436.17 20.75*

Style 1 17.18 17.18 0.82

Phase 3 2786.49 928.83 44.14"

Phase vs Style 3 558.56 186.19 8.85*

Error 112 2356.82 21.04

Total 135 10350.02

* p < .05

45

Table 6. ANOVA Table - Erector Spinae (% MDA)

Source df ss ms f ratio

Subject 16 1019.08 63.69 2.46*

Style 1 154.47 154.47 5.96*

Phase 3 6460.06 2153.35 83.11"

Phase vs Style 3 1263.76 421.25 26.26*

Error 112 2902.00 25.91

Total 135 11799.37

* p < .05

46

Table 7. ANOVA Table - Latissimus Dorsi (% MVIC)

Source df ss ms f

r a t i 0

Subject 16 322.65 20.17

37. 12

Style 1 0.77 0.77

1.43

Phase 3 78.83 26.28

*p< .05

47

Table 8. ANOVA Table - Latissimus Dorsi (% MDA)

Source df ss ms f ratio

Subject 16 629.96 39.37 2.36"

Style 1 1.12 1.12 0.07

Phase 3 6832.84 2277.61 136.78*

Phase vs Style 3 98.44 32.81 1.97

Error 112 1864.92 16.65

Total 135 9427.27

* p < .05

48

Table 9. ANOVA Table - Gluteus Maximus (% MVIC)

Source df ss ms f ratio

Subject 16 2456.24 153.52 20.96*

Style 1 4.74 4.74 0.65

Phase 3 111.25 37.08 5.06

Phase vs Style 3 22.07 7.36 1.00

Error 112 820.46 7.33

Total 135 3414.78

* p < .05

49

Table 10. ANOVA Table - Gluteus Maximus (% MDA)

Source df ss ms f ratio

Subject 16 906.07 56.63 1.24

Style 1 5.25 5.25 0.12

Phase 3 1793.72 597.91 13.12

Phase vs Style 3 236.14 78.71 1.73

Error 112 5103.44 45.57

Total 135 8044.62

* p < .05

50

Table 11. ANOVA Table - Biceps Femoris (% MVIC)

Source df ss ms f ratio

Subject 16 2050.58 128.16 15.17*

Style 1 0.73 0.73 0.09

Phase 3 212.14 70.71 8.37*

Phase vs Style 3 64.18 21.39 2.53

Error 112 946.07 8.45

Total 135 3273.70

* p < .05

51

Table 12. ANOVA Table - Biceps Femoris (% MDA)

Source df ss ms f ratio

Subject 16 1238.54 77.41 1.11

Style 1 3.34 3.34 0.05

Phase 3 1088.19 362.73 5.20

Phase vs Style 3 326.40 108.80 1.56

Error 112 7805.51 69.69

Total 135 10461.99

* p < .05

52

Table 13. ANOVA Table - Semitendinosus (% MVIC)

Source df ss ms f ratio

Subject 16 1290.64 80.66 37.98*

Style 1 3.11 3.11 1.46

Phase 3 18.73 6.24 2.94

Phase vs Style 3 12.88 4.29 2.02

Error 112 2.12 0.02

Total 135 1327.48

* p < .05

53

Table 14. ANOVA Table - Semitendinosus (% MDA)

Source df ss ms f ratio

Subject 16 2616.93 163.56 4.60*

Style 1 19.01 19.01 0.53

Phase 3 407.28 135.76 3.81

Phase vs Style 3 308.01 102.67 2.88

Error 112 3986.33 35.59

Total 135 7337.55

* p < .05

54

Results

Rectus Abdominal Muscles

% MVIC. The EMG activity of the rectus abdominis muscle

was greatest early in the lift and decreased as the lift

progressed (tab. 15; fig. 7). Differences (p < .05) were

found between subjects and between quarters within a lift

style (tab. 1). No difference (p < .05) were found when

comparing EMG activity in each quarter between the lifting

styles. The first quarter EMG activity was larger (p<.05)

than quarters 2, 3 and 4 in the lordotic style of lifting

(fig. 6). The second quarter EMG activity was greater (p<.05)

than that found in the third or fourth quarter in the lordotic

and kyphotic styles of lifting. No differences were found in

EMG activity between quarters 1 and 2 of the kyphotic lift or

between quarters 3 and 4 of either lifting style.

% MDA. There were differences (p<.05) between individual

subjects and between quarters within a lift style (tab. 2).

Quarter 1 is larger (p<.05) than quarter 2, quarter 3 or

quarter 4 in the lordotic lift. In the kyphotic lift no

difference was noted between quarter 1 and quarter 2, however

quarter 1 and quarter 2 were larger (p<.05) than quarter 3 or

quarter 4 (tab. 16, fig 8), this was also true in the lordotic

lift as well. No difference in EMG activity was found between

quarter 3 and quarter 4 in either lift style. Comparison of

55

Table 15. EMG Activity (% MVIC) - Rectus Abdominis

Style/Phase N MEAN SEMEAN MIN MAX

Lordosis

Quarter 1 17 2.05 0.30 0.55 5.11

Quarter 2 17 1.78 0.26 0.54 3.59

Quarter 3 17 1.53 0.21 0.43 3.11

Quarter 4 17 1.40 0.19 0.47 2.39

Kyphosis

Quarter 1 17 1.98 0.28 0.46 4.27

Quarter 2 17 1.80 0.28 0.57 4.62

Quarter 3 17 1.52 0.22 0.52 3.56

Quarter 4 17 1.53 0.24 0.55 5.11

56

3 Rectus AbdominisI KyphosisS Quiet

_ A Lordosis

•I I

0 1 2 ,3 4

Quarter of Lift Cycle

Figure 7. EMG Activity (% MVIC) Rectus Abdominis. Note thequiet file has nearly the same amplitude of activity asthe lift.

57

Table 16. EMG Activity (% MDA) - Rectus Abdominis

Style/Phase N MEAN SEMEAN MIN MAX

Lordosis

Quarter 1 17 39.25 1.50 27.85 53.01

Quarter 2 17 33.50 1.17 24.64 41.57

Quarter 3 17 29.08 1.33 16.39 38.45

Quarter 4 17 27.37 1.10 17.97 34.99

Kyphosis

Quarter 1 17 35.36 1.67 21.73 46.08

Quarter 2 17 33.13 1.62 21.12 48.83

Quarter 3 17 28.43 1.33 16.21 36.25

Quarter 4 17 27.82 1.45 15.10 39.13

58

50 Rectus AbdominisT~ ~ aaaa L, Ct LCZ aa LaLaa La

<1 I Kyphosis

I A Lordosis

acip L@ aftaaai@aa ;a La a' aaa(;a@ Laaa(;aa@aa Laaaaaaaac Ltq Laaaa Laead daq

12 3 4

Quarter of Lift Cycle

Figure 8. EMG Activity (% MDA) Abdominal Obliques.

59

EMG activity between the two lifting styles within a quarter

found a difference only in the first quarter (p<.05) with the

lordotic lift having the greater EMG activity (fig. 2).

Abdominal Oblique Muscles

% MVIC. Abdominal oblique EMG activity was greatest in

the early phases of the lifts in both the lordotic and

kyphotic styles of lifting (fig. 9; tab. 17). Differences

(p<.05) were found between individual subjects and between

quarters within a lifting style (tabs. 3). The EMG activity

in the first quarter was larger (p<.05) than that found in

quarters two, three and four in both the lordotic and kyphotic

style of lifting. The EMG activity in quarter two was greater

(p < .05) than that found in quarters three and four. No

difference (p<.05) in EMG activity was found between quarters

three and four in either style of lifting. No significant

differences were noted in EMG activity when comparing lordotic

vs. kyphotic postures in each quarter of the lift cycle.

% MDA. The results of the % MDA analysis were identical

to that found in the % MVIC analysis. Differences (p<.05)

were found between individual subjects and between quarters

within a lifting style (tab. 4). The greatest EMG activity

was found in the first quarter of the lift which decreased as

the lift progressed regardless of lifting style (fig. 10, tab.

18). EMG activity in the first quarter was larger (p<.05)

60

Table 17. EMG Activity (% MVIC) - Abdominal Obliques

Style/Phase N MEAN SEMEAN MIN MAX

Lordosis

Quarter 1 17 2.41 0.45 0.75 7.78

Quarter 2 17 1.99 0.37 0.73 5.57

Quarter 3 17 1.63 0.28 0.58 4.29

Quarter 4 17 1.59 0.28 0.57 4.36

Kyphosis

Quarter 1 17 2.33 0.33 0.84 5.82

Quarter 2 17 1.91 0.30 0.67 5.35

Quarter 3 17 1.68 0.29 0.57 5.04

Quarter 4 17 1.51 0.24 0.55 4.13

61

Abdominal Obliques* Kyphosis* Quiet

S-A Lordosis

- A 1

7

0 1 2 3 4

Quarter of Lift Cycle

Figure 9. EMG Activity (% MVIC) Abdominal Obliques. Ncethat the quiet EMG amplitude is nearly the same as theamplitude during the lift.

62

Table 18. EMG Activity (% MDA) - Abdominal Obliques

Style/Phase N MEAN SEMEAN MIN MAX

Lordosis

Quarter 1 17 40.22 1.48 30.41 49.37

Quarter 2 17 33.26 1.04 26.25 40.47

Quarter 3 17 27.99 0.98 19.34 35.15

Quarter 4 17 26.96 0.64 20.20 30.14

Kyphosis

Quarter 1 17 37.48 1.20 26.38 44.73

Quarter 2 17 32.38 0.97 22.63 38.27

Quarter 3 17 27.98 1.29 14.87 35.12

Quarter 4 17 26.39 1.46 13.30 35.51

63

Abdominal Obliques

A,, I Kyphosis

A Lordosis

0

Quarter of Lift Cycle

Figure 10. EMG Activity (% MDA) Abdominal Obliques.

64

than that found in quarter two, quarter three, or quarter

four. EMG activity in quarter two was larger (p<.05) than

that found in quarter three or quarter four. No difference

was found in EMG activity between quarter 3 or quarter 4. No

difference was found when comparing the EMG activity in each

quarter of the lordotic lift against the EMG activity recorded

in the same quarter of a kyphotic.

Erector Spinae Muscles

% MVIC. Erector spinae muscle EMG activity was greatest

in the early stages of the lift and decreased throughout the

lift in both styles of lifting. The level of EMG activity was

greater in quarter one and less in quarter 4 in the lordotic

lift (tab. 19; fig. 11). EMG activity in quarter one was

greater (p<.05) than that found in quarter 2, quarter 3, or

quarter 4 in both styles of lifts (tab. 19; fig. 11). The EMG

activity in quarter two was also greater (p < .05) than that

found in quarters three and four for both styles of lift. The

EMG activity in the third quarter was larger (p<.05) than

quarter four in both lifts. Difference were found in EMG

activity between subjects, between quarters and with the

timing of EMG activity in the two styles of lifting (style vs

quarter) (tabs. 5, 6). Comparing the EMG activity between the

two lifting styles in each quarter found the lordotic lift

having more activity (p<.05) in the first quarter and less

65

Table 19. EMG Activity (% MVIC) - Erector Spinae

Style/Phase N MEAN MEDIAN SEMEAN MIN MAX

Lordosis

Quarter 1 17 26.83 21.99 3.50 10.17 69.74

Quarter 2 17 20.89 17.75 2.40 7.73 47.01

Quarter 3 17 13.23 11.77 1.35 5.81 28.21

Quarter 4 17 10.10 9.26 0.88 4.41 15.85

Kyphosis

Quarter 1 17 21.05 16.81 2.32 8.38 41.56

Quarter 2 17 17.80 16.25 1.96 7.69 38.51

Quarter 3 17 15.70 14.05 1.37 6.05 28.82

Quarter 4 17 13.83 14.51 1.52 5.64 30.69

66

Erector SpinaeM Kyphosis* Quiet

T A Lordosis

> L

nU

< 10~

0

0 1 2 3 4

Quarter of Lift Cycle

Figure 11. EMG Activity (% MVIC) - Erector Spinae. Note thedifference in amplitude between the quiet file andlifting files.

67

activity in the fourth quarter than the kyphotic lift. No

differences were found in quarter 3 or quarter four.

% MDA. Differences (p<.05) were found between individual

subjects, between lifting styles in the same quarter, between

quarters, and in the quarter-lift style interaction (tab. 6).

The EMG activity in quarter one is greater (p<.05) than that

,und in quarter two, quarter three or quarter four in the

lordotic and kyphotic styles of lifts (fig. 12). The activity

in quarter two is also larger (p<.05 ) than that found in

quarter three in the lordotic lift but not the kyphotic lift

(fig. 6; tab. 20). Quarter two and three had greater EMG

activity (p<.05) than that found in quarter four in both

lifting styles (fig. 12; tab. 20). The EMG activity (% MDA)

was greater (p < .05) during the third quarter in the kyphotic

lift. Comparing EMG activity of the two lifting styles in the

same quarter found differences (p<.05) in the first quarter,

where the lordotic style was greater and in the third and

fourth quarters where the kyphotic style had greater activity

(fig 12; tab. 20).

68

Table 20. EMG Activity (% MDA) - Erector Spinae

Style/Phase N MEAN SEMEAN MIN MAX

Lordosis

Quarter 1 17 42.95 0.94 34.62 50.07

Quarter 2 17 33.89 1.01 26.07 39.43

Quarter 3 17 22.18 1.11 17.15 32.75

Quarter 4 17 17.70 1.30 9.82 31.34

Kyphosis

Quarter 1 17 36.66 1.58 19.01 46.23

Quarter 2 17 32.84 1.25 18.31 39.89

Quarter 3 17 29.76 1.41 18.11 38.23

Quarter 4 17 25.98 1.88 13.51 40.38

69

Erector Spinae

40_ A

I KyphosisA Lordosis

- 0 1

Quarter of Lift Cycle

Figure 12. EMG Activity (% MDA) - Erector Spiriae.

70

Latissimus Dorsi Muscle

% MVIC. EMG activity was greatest in the first quarter

and decreased in each subsequent quarter (fig. 13; tab. 21).

Differences (p<.05) were found between subjects and between

quarters within a style of lifting (tab. 7). The first

quarter had greater EMG activity than quarter two, quarter

three or quarter four in both styles of lifting. Quarter two

also had greater (p<.05) EMG activity than quarters three or

four in both styles of lifting (fig. 13; tab. 21). No

difference (p<.05) was found in the EMG activity between

quarters three and four in either style of lifting (fig. 13;

tab. 21). No differences were found when comparing the

lordotic and kyphotic lift in each quarter (fig. 13; tab. 21).

% MDA. Followed a similar pattern to that reported for

% MVIC. Differences (p<.05) were noted between subjects and

between quarters wiLhin a lifting style. No differences were

found between lifting styles, nor was a style-quarter

interaction found. EMG activity was greatest in quarter one

and decreased in each subsequent quarter. Quarter one had

greater (p<.05) activity than that found in quarter two,

quarter three or quarter four (fig. 14; tab. 22). Quarter two

had higher activity (p<.05) than quarters three or four (fig.

14; tab. 22). Quarter three had more EMG activity than

quarter four in the lordotic lift, but not in the kyphotic

lift (fig. 14, tab. 22).

71

Table 21. EMG Activity (% MVIC) - Latissimus Dorsi

Style/Phase N MEAN SEMEAN MIN MAX

Lordosis

Quarter 1 17 4.27 0.57 1.38 9.57

Quarter 2 17 3.43 0.44 1.21 6.79

Quarter 3 17 2.48 0.32 0.72 5.45

Quarter 4 17 2.15 0.29 0.69 4.94

Kyphosis

Quarter 1 17 3.99 0.58 1.09 10.76

Quarter 2 17 3.22 0.44 0.96 7.41

Quarter 3 17 2.42 0.31 0.89 5.37

Quarter 4 17 2.15 0.30 0.71 5.08

72

Latissimus Dorsi5 Kyphosis

T * QuietA Lordosis

4

A 'A

Quarter of Lift Cycle

Figure 13. EMG Activity (% MVIC) - Latissimus Dorsi. Notethat the EMG activity during the lift is the same as thequiet file in the latter stages.

73

Table 22. EMG Activity (% MDA) - Latissimus Dorsi

Style/Phase N MEAN SEMEAN MIN MAX

Lordosis

Quarter 1 17 40.94 1.30 30.87 49.29

Quarter 2 17 33.49 0.96 27.58 41.16

Quarter 3 17 23.92 0.85 17.41 31.11

Quarter 4 17 20.88 0.89 14.23 29.70

Kyphosis

Quarter 1 17 38.26 1.58 24.58 48.35

Quarter 2 17 32.67 0.80 26.05 39.19

Quarter 3 17 25.10 0.84 16.08 32.26

Quarter 4 17 22.45 1.11 12.37 33.60

74

Latissimus Dorsi45 r

<2 4oj ..

.- ....... .

o

U Kyphosis_ A Lordosis

Z 1 2 3 4

Quarter of Lift Cycle

Figure 14. EMG Activity (% MDA) - Latissimus Dorsi.

. .... m . . . .. .

75

Gluteus Maximus Muscle

% MVIC. Gluteus maximus muscle EMG activity reached a

maximum intensity in quarters two and three and was less in

quarter one and quarter four (tab. 23; fig. 15). Differences

(p<.05) in EMG activity were found between subjects and

between quarters within each style of lifting (tabs 15). No

differences (p<.05) in EMG activity were seen when comparing

the two styles of lifting against each other in each quarter

(tabs. 9; figs. 15). EMG activity was greater (p<.05) in

quarter two than quarter one in the lordotic and kyphotic

lifts. Quarter three had greater EMG activity than quarter

one in the lordotic lift but not in the kyphotic lift. No

difference was noted in intensity of EMG activity between

quarter one and quarter four or between quarters two and three

in either the lordotic or kyphotic lift (fig. 15). Quarters

two and three had greater (p<.05) EMG activity than quarter

four in the kyphotic, but not in the lordotic lift (fig. 15).

% MDA. A similar pattern of EMG activity was seen using

% MDA analysis. Differences were noted between subjects and

quarters, but not between lifting styles (tab. 10). Quarter

one had less (p<.05) EMG activity than quarters two and three

in both styles of lifting and less than quarter four in the

lordotic style (fig. 16; tab. 24). No differences (p<.05)

were noted between quarters two and three in either lifting

style, or between quarter two and four in the lordotic style

76

Table 23. EMG Activity (% MVIC) - Gluteus Maximus

Style/Phase N MEAN SEMEAN MIN MAX

Lordosis

Quarter 1 17 8.88 1.38 1.31 20.03

Quarter 2 17 10.88 1.47 2.16 26.00

Quarter 3 17 11.30 1.16 5.10 20.26

Quarter 4 17 10.40 1.37 4.10 25.16

Kyphosis

Quarter 1 17 9.07 1.13 2.55 19.37

Quarter 2 17 11.18 1.21 6.00 25.59

Quarter 3 17 10.91 0.96 5.02 20.51

Quarter 4 17 8.77 1.02 3.35 22.09

77

Gluteus Maximus20

* Kyphosis

* QuietALordosis

>5

I'-7

0I0 1 2

Qure fLf yl

Fiur 1. GAcivty(%I C - ltu ai u

78

Table 24. EMG Activity (% MDA) - Gluteus Maximus

Style/Phase N MEAN SEMEAN MIN MAX

Lordosis

Quarter 1 17 26.49 2.03 9.01 38.53

Quarter 2 17 34.09 1.88 14.54 46.26

Quarter 3 17 37.00 1.43 25.75 50.18

Quarter 4 17 31.88 1.61 20.24 43.74

Kyphosis

Quarter 1 17 28.59 2.00 9.51 39.23

Quarter 2 17 36.07 1.51 25.03 47.52

Quarter 3 17 35.59 1.15 24.71 41.16

Quarter 4 17 27.63 1.48 15.71 39.68

m m . m m m muW

79

Gluteus Maximus

40

.. ;: ~A -- ---- ........-----

20

- U Kyphosis

A Lordosis10

0 I I I

0 2 3 4

Quarter of Lift Cycle

Figure 16. EMG Activity (% MDA) - Gluteus Maximus.

80

(fig 16; tab. 24). Quarter three had higher (p<.05) values

of EMG activity than quarter four in the lordotic and kyphotic

lifts (fig. 10). Quarter two had increased (p<.05) EMG

activity over quarter four in the kyphotic lift but not the

lordotic lift (fig. 16; tab. 24).

Biceps Femoris

% MVIC. Biceps femoris muscle EMG activity was at its

minimal level in quarter one and increased in iatensity

throughout the remaining three quarters of the lordotic lift

(tab. 25; fig. 17). In the kyphotic lift the EMG activity

increased from quarter one to quarter three and then decreased

in quarter four (tab. 25; fig. 17). Differences (p < .05) in

EMG activity were found between subjects and between quarters

within a lift (tab. 11). The lordotic lift had greater

(p<.05) EMG activity in quarter four, but no other differences

(p<.05) were found between styles when compared in the same

quarter of a lift (tab. 11). No difference in EMG activity

was found between the first two quarters in the lordotic lift

(tab. 25; fig. 17). Differences (p<.05) were found in the EMG

activity between the first and third quarters in both lifting

styles and between the first and fourth in the lordotic lift

(fig. 17). Differences (p<.05) in EMG activity were found

81

Table 25. EMG Activity (% MVIC) - Biceps Femoris

Style/Phase N MEAN SEMEAN MIN MAX

Lordosis

Quarter 1 17 5.23 0.75 2.43 14.93

QuartEr 2 17 5.84 0.73 2.70 14.13

Quarter 3 17 8.28 1.61 2.39 29.32

Quarter 4 17 8.73 1.62 2.16 27.29

Kvrhosis

82

15 Biceps Femoris* Kyphosis

* Quiet> Lordosis

10T

TT

0 1 234

Quarter of Lift Cycle

Figure 17. EMG Activity (% MVIC) - Biceps Femoris.

83

between the third and fourth quarters in the kyphotic lift,

but not in the lordotic lift (fig. 17).

% MDA. A similar pattern was seen when doing the % MDA

analysis of EMG activity. Differences (p<.05) were seen

between subjects and between quarters within a lift style

(tab. 12). No differences (p<.05 ) were seen between quarters

one and two in either style of lift (tab. 26; fig. 18).

Quarter one had less (p<.05) EMG activity that quarter three

in both lifting styles (fig. 18). Quarter four had greater

(p<.05) EMG activity than quarter one and two in the lordotic

lift, but no difference was found in the kyphotic lift (tab.

26; fig. 18). No difference (p<.05) in EMG activity was seen

between quarter one and four in the lordotic lift or between

quarters two and three in both styles of lifting, while

quarter four had a higher level in the kyphotic lift (fig.

18).

Semitendinosus

% MVIC. Differences (p<.05) in EMG activity were found

between subjects, and between quarters of the lift (tabs. 13).

No difference (p<.05) in EMG activity was found between

quarters one and four and quarters one and two regardless of

lifting style (tab. 27; fig. 19). A difference (p<.05) in EMG

activity was found between quarters one and three in the

lordotic lift but not in the kyphotic lift (fig. 19; tabs.

84

Table 26. EMG Activity (% MDA) - Biceps Femoris

Style/Phase N MEAN SEMEAN MIN MAX

Lordosis

Quarter 1 17 23.02 2.56 11.41 39.57

Quarter 2 17 24.99 2.02 12.68 37.60

Quarter 3 17 30.56 1.50 21.14 44.31

Quarter 4 17 30.44 2.28 15.09 44.26

Kyphosis

Quarter 1 17 23.39 2.16 9.01 39.91

Quarter 2 17 27.77 1.75 16.78 41.27

Quarter 3 17 31.62 1.42 15.16 41.15

Quarter 4 17 24.98 2.34 4.30 40.54

85

Gluteus Maxirnus

40!

'A< ii

20

4) IKyphosis

ALordosis10

0°I y i0 1 2 3 4

Quarter of Lift Cycle

Figure 18. EMG Activity (% MDA) - Biceps Femoris

86

Table 27. EMG Activity (% MVIC) - Semitendinosus

Style/Phase N MEAN SEMEAN MIN MAX

Lordosis

Quarter 1 17 4.04 0.60 0.37 8.84

Quarter 2 17 4.43 0.67 0.36 9.31

Quarter 3 17 5.35 1.02 0.37 14.75

Quarter 4 17 4.96 0.97 0.37 14.02

Kyphosis

Quarter 1 17 4.77 0.82 0.38 11.24

Quarter 2 17 5.35 0.89 0.39 12.54

Quarter 3 17 5.44 0.97 0.37 14.04

Quarter 4 17 4.32 0.85 0.37 12.03

87

8 Semitendinosus

T

Quarter u iCet

Figre 9. MG ctvit (%KVI) Lortedioss.

88

27). No differences (p<.05) were found between quarters two

and three in either style of lift, or between quarters two and

four and quarters three and four in the lordotic lift (fig.

13). Differences were found (p<.05) between quarters two and

four and between quarters three and four in the kyphotic lift

(tab. 27; fig 13).

% MDA. Differences (p<.05) were seen between subjects,

between quarters within a lifting style and in the timing of

EMG activity (lift vs style interaction) (tab. 14). No

differences were found between quarters one and two or between

quarters two and three in either style of lift (fig. 14).

Differences (p<.05) were found between quarters two and four,

quarters one and four and quarter three and four in the

kyphotic lift and between quarter one and quarter three in the

lordotic lift (fig. 14). No other differences were found.

. .. p . .. .. . .

89

Table 28. EMG Activity (% MDA) - Semitendinosus

Style/Phase N MEAN SEMEAN MIN MAX

Lordosis

Quarter 1 17 29.46 2.17 12.58 44.27

Quarter 2 17 30.27 1.73 18.57 44.79

Quarter 3 17 33.55 1.45 22.38 46.73

Quarter 4 17 30.83 1.77 20.31 45.22

Kyphosis

Quarter 1 17 30.45 1.90 15.56 44.23

Quarter 2 17 33.06 1.51 20.39 44.69

Quarter 3 17 32.01 1.28 21.77 42.91

Ouarter 4 17 25.60 1.95 14.72 42.88

90

40 SemitendinosusT

'C I -- -

U Kyphosis

A Lordosis

02 3 4

Quarter of Lift Cycle

Figure 20. EMG Activity (% MDA) - Semitendinosus.

91

Discussion

This study used two methods of quantifying EMG activity,

percent of maximal voluntary isometric contraction (% MVIC)

and percent of maximum intensity during activity (% MDA).

The quantification of EMG as % MVIC allows comparisons of EMG

signal intensity between different muscle groups. This

comparison can help determine which muscle group is most

active during an activity. However, there are problems that

must be considered when using % MVIC as the referencing

standard. Problems include: using an isometric contraction

to standardize a dynamic event, proper joint angle and testing

procedure to get the maximum EMG signal, and subject

motivation and effort. Use of % MDA to quantify EMG signals

reveals the EMG activity pattern of each muscle. Comparison

of signal intensity between different muscles is not possible,

since each muscle is normalized against its own EMG signal

during the activity and there is no way to know the absolute

intensity of the signal recorded. However, advantages exist

for the use of % MDA as a referencing standard. Among its

advantages are: dynamic referencing standard (the EMG signal

used for normalization is recorded during the actual

activity), eliminates problems with subject motivation and

choosing of the proper joint angle and testing procedure for

92

maximum EMG signal. For the most part, the two methods of

analysis yielded similar results during this study.

This study investigated squat lifting and the effect

varying the lumbar posture had on the EMG activity of the hip

extensor (GM, BF, and ST) muscles and trunk muscles (RA, AO,

ES, and LD). The muscles were chosen because of: anatomical

connections to the thoracolumbar fascia, and potential

contributions to a lift. A successful squat lift involves

raising an object and keeping it under control until

completion of the lift. The initial portion of the lift plays

the largest role in the success or failure of the lift. It

is in the initial portion of the lift that the inertia of the

load is overcome and the greatest stress is placed on the

lumbo-sacral spine (Frievalds, 1984). Therefore, differences

in EMG activity observed during this period, or between the

first period and subsequent periods carries the greatest

significance. This discussion will center on differences

between styles in the first quarter and differences between

the first quarter and subsequent quarters within a single

style of lift.

Two distinct patterns of EMG activity, independent of

lumbar spine posture, were seen in this study: 1) a trunk

muscle pattern (LD, AO, RA, and ES) which showed more EMG

activity in the early portions of the lift cycle and

93

decreasing intensity as the lift progressed (figs. 7-14), and

2) a hip extensor pattern for which the hip extensor muscles

(GM, BF, ST) had their lowest level of EMG activity in the

first quarter, which increased in the second and third

quarters, before levelling off or decreasing in the last

quarter (figs. 15-20). Generally, the patterns of EMG

activity of the ES and AO seen during this study were

consistent with the patterns reported by other researchers

(Delitto, 1985; Hart 1987). This study differed from other

studies in that all trunk muscles (ES, AO, RA, and LD) showed

greatest EMG activity in the first quarter. The EMG activity

decreased as the lift in each of the following phases.

Delitto (1985) found this pattern in the AO muscle and the ES

muscle in a lordotic lift, but not in the kyphotic lift. In

the kyphotic lift the ES EMG activity began at a lower level

(when compared to the same time period in the lordotic lift)

and increased during the lifting cycle (Delitto, 1985). One

possible reason for the different ES EMG patterns may be the

procedures used to determine starting and ending points for

the lift cycle. Delitto (1985) used a pressure-sensitive

switch to indicate the beginning of the lift, and a single

axis electrogoniometer secured at the hip to indicate the end

of the lift. This study used video data to determine starting

and ending points. Therefore, the lift cycle may be of

different lengths in the different studies. This might cause

the normalization of the lift cycle and EMG activity to not

94

be exactly equivalent. The trunk muscles produced similar

EMG activity patterns (% MVIC and % MDA), regardless of the

style of squat lifting. However, the EMG activity recorded

in the RA, AO and LD appears to indicate a relatively minor

contribution to the success of the lift (fig. 7, 9, 13). The

RA EMG activity (% MVIC) during the lift did not differ

significantly from that recorded during quiet standing in any

time period of the lift (fig. 7). The AO and LD EMG activity

(% MVIC) did not differ from quiet standing in quarters three

or four (fig. 9, 13). Thus, the contributions of the AO, RA

and LD is finished by the half-way point of the lift.

In the hip extensor muscles the pattern of EMG activity

differed from that seen in the trunk muscles. The EMG

activity in the hip extensor muscles studied (GM, BF and ST)

was lowest in the first quarter (figs. 15-20). The activity

increased through quarters two and three, before plateauing

or decreasing in the final quarter. No differences were seen

in hip extensor muscle EMG activity between the two lifting

styles in the first three quarters. It was not until the

fourth quarter that differences were seen between the two

lifting styles. The BF (% MVIC) and tha ST (% MDA) showed

greater EMG activity in the lordotic lift during the fourth

quarter. The ST also showed a different (p<.05) relationship

between timing and EMG (% MDA) activity (style vs. quarter).

These results do not show the hip extensor muscles (GM, BF,

95

and ST), acting through the thoracolumbar fascia, as providing

any greater contribution in the kyphotic lift when compared

to the lordotic lift under the test conditions of this study.

In this study, only the ES muscle showed differences

between the two lifting styles during the initial period of

the lift. All other muscles, trunk (RA, LD, AO) and hip

extensor (GM, ST, BF), showed similar patterns of EMG activity

regardless of lumbar posture until the end of the lift.

Plotting the ES EMG activity revealed different shapes of EMG

activity in the two lifting styles (Figs. 13, 14). In the

lordotic lift the decrease of the EMG activity took on a

sigmoidal shape while in the kyphotic lift the EMG activity

decreased in a gentle arc. The lordotic style had greater EMG

activity in the first quarter while in the third and fourth

quarters the activity in the kyphotic lift was greater.

It has been speculated that the decreased ES EMG activity

during the early stages in the kyphotic lifting style may be

due to greater efficiency of the ES muscles because of the

muscles being in a prestretched condition (Delitto, 1985).

However, this does not appear to be the case. It appears that

a different ES muscle activity pattern is employed in the

kyphotic lift. Using % MDA to normalize the EMG activity

revealed the relative contribution of each muscle compared to

its peak amplitude during the activity. If differences seen

in the first quarter (% MVIC) were primarily due to increased

96

efficiency of the ES muscles, then a similar muscle activity

pattern should have been seen (% MDA) in the lordotic and

kyphotic lifts. This was not observed in the ES, therefore,

it was concluded that different mechanisms were at work in the

two lifting styles.

The remaining trunk muscles (RA, AO, and LD) revealed

similar patterns of EMG activity in the lordotic and kyphotic

lifting styles. The activation of these muscles was minimal

(< 5% of MVIC) indicating that their role in providing

stability to the spine during the lift may be limited. This

low activity of the RA and AO is consistent with the results

reported by other researchers and suggests that the role of

intra-abdominal pressure as a support mechanism may not be as

great as thought (Ekholm, 1982; Hemborg, 1983; & McGill 1987,

1990). The low level of activity suggest that any

contributions of these muscles to the lift through the

thoracolumbar fascia may also be limited. Delitto (1985)

showed greater activation of the AO muscles during both styles

of lifting. This may be due to using a different method of

normalizing the muscle activity during the lift.

Lindh (1989), Hart (1987) and Adams (1980) report that

in a kyphotic (i.e. flexed) posture the ligaments are on a

stretch and provide counterbalancing force to the trunk. Hart

(1987) termed this phenomenon as 'hanging on ligaments'. A

97

potential danger of ligamentous support is that the forces

produced by ligaments generally have a shorter lever arm than

the muscle forces so they may be subject to extremely high

loads if they are the main support during a lift (Lindh,

1989). To protect the ligaments and the spine, ES muscles

should be active at the beginning of the lift, but no motion

of the spine should occur until the inertia of the load is

overcome (Davis, 1965; Lindh, 1989). After the initial

inertia of the load is overcome the spine extends to the end

of the lifting cycle (Davis, 1965).

In this study it was observed that the ES EMG activity

is higher in the lordotic lift during the first quarter when

compared to the kyphotic lift, no differences were seen in the

other trunk muscles or the hip extensor muscles. The clinical

implications are that lifting with the lumbar spine in a

lordotic position is advantageous. The increased EMG activity

of the ES muscles in a lordotic lift causes increased

compression across the lumbo-sacral joint (Frievalds, 1984).

However, the lumbar spine provides more resistance to

compressive forces than bending forces and is better able to

deal with increased compression (Lin, 1978). Also, with the

lumbar spine in a lordotic posture the ligaments are not on

stretch and the antiflexion moment is provided to a greater

extent by muscle contraction thus protecting the ligaments

from excessive strain (Hart, 1987; Lindh, 1989). These

98

factors may help explain why decreased isometric endurance of

the back extensor muscles is a predictor of low back pain

(Beiring-Sorensen, 1989). A person may not have the endurance

needed to protect the ligaments and the lumbar spine from

undue stress when doing repetitive lifting.

In the later stages of the lift (quarters three and four)

the ES EMG activity is greater in the kyphotic lift and the

hip extensor activity (GM, BF, and ST) is greater in the

lordotic lift. This activity may contribute to the final

restoration of the upright posture. In the lordotic lift the

spine should already be in a lordotic posture and ES muscle

activity is not needed to restore the normal lordotic curve.

Final restoration of upright posture may be accomplished

through hip extension. The increased ES activity observed In

the kyphotic lift may be a result of the restoration of the

normal lordotic curve. Lumbar extension is needed for the

final attainment of the fully upright posture in the kyphotic

lift.

99

CHAPTER 5

SUMMARY AND CONCLUSION

Summary

The purpose of this study was to determine the function

of muscles that are anatomically related to the thoracolumbar

fascia and lumbar spine during a squat lift and to see the

effects of varying the lumbar posture. The research

hypothesis was that lifting in a kyphotic posture would result

in greater EMG activity in the hip extensor muscles. The hip

extensor muscles were thought to be anatomically situated to

extend the trunk. Seven muscles (RA, AO, ES, LD, GM, BF, ST),

were chosen for this study because of their attachment to the

thoracolumbar fascia and posterior ligamentous system.

Seventeen male subjects recruited from the University of

Kentucky performed three squat lifts in each of the lumbar

postures. Each lift was normalized to a percentage of total

time and divided into four equal parts. Likewise, the EMG

activity recorded in each muscle was also normalized. Two

methods of normalization were used: 1) a percentage of the

muscle's maximum isometric contraction (% MVIC) and 2) a

percentage of the maximum EMG activity recorded in that muscle

during the lift (% MDA). Analysis revealed two distinct

patterns of EMG activity: a trunk muscle pattern and a hip

extensor muscle pattern. In the trunk muscle pattern greatest

100

activity was observed in the first quarter. This activity

decreased as the subject moved from the squat position to the

upright position. In the hip extensor muscle pattern the

smallest amount of EMG activity was observed in the first

quarter. The EMG activity increased in the second and third

quarters before leveling off or decreasing in the fourth

quarter. A 2 X 4 repeated measure ANOVA was used to

statistically analyze the EMG activity recorded in each

muscle. Lumbar posture (lordotic vs. kyphotic) and timing

(quarter 1, quarter 2, quarter 3, and quarter 4) were analyzed

for each muscle. Analysis revealed differences between

subjects and between different time phases within a style of

lifting. No differences were observed during the early stages

of the lift when comparing the two styles in any muscle except

the ES muscles. Therefore, the research hypothesis is

rejected and the null hypothesis accepted.

Conclusions

1) Two distinct patterns of EMG activity were seen in this

study: a trunk muscle (RA, AO, ES, LD) pattern and a hip

extensor muscle (GM, BF, ST) muscle pattern.

2) In the early stages of the lift no difference was seen in

the hip extensor (GM, BF, ST) EMG activity between the

two lifting styles.

101

3) Different ES EMG activity patterns were seen when

comparing the different lifting styles. Less EMG

activity was seen in the first quarter with the lumbar

spine in a kyphotic (flexed) posture, when compared to

the lordotic (extended) posture. It is thought that more

of the load is being borne by the ligaments in the

kyphotic. Conversely, the increased activity seen with

the lordotic lift suggest that more of the load is being

supported by the muscles.

4) It appears that the main function of the trunk muscles and

the posterior ligamentous system is to provide stability

to the lumbar spine during a lift, especially the early

stages, i.e. until the inertia of the load is overcome.

5) The trunk muscles (AO, RA, LD), other than the ES, play

a relatively minor role in the squat lift, regardless of

the posture.

6) clinically, lifting with the lumbar spine in a lordosis

is advantageous. The muscles appear to bear more of the

load in providing stability to the spine and the muscles

thereby protect the inert tissues. However, there are

increased compressive forces on the lumbar spine in this

posture, but the lumbar spine can withstand compressive

forces better than shear or torsion forces.

102

Recommendations for future study.

This study did not reveal any difference in EMG activity

between the two lifting styles except in the ES muscles. It

is possible that the weights chosen were not heavy enough to

show a difference. Heavier loads could be used in future

studies to see if different EMG patterns are seen. In

addition, analysis of repeated lifts or lifting after the

muscles are fatigued, should be done as this may more closely

simulate the work environment. Video analysis of the subjects

while they are lifting, in conjunction with the EMG, so that

the EMG activity patterns can be coordinated with the

movements.

103

APPENDIX A

104

Consent for Research Study

"EMG Activity of selected lumbar and hip muscle during a

Squat Lift: Effect of Varying the Lumbar Posture"

I, _, freely and

voluntarily agree to participate in a thesis research project

under the direction Jim Vakos, Dr. Arthur Nitz, Dr. Joseph

Threlkeld, and Dr. Rob Shapiro. This project is to be

conducted at Wenner-Gren Biomechanics Laboratory at the

University of Kentucky.

I understand that knowledge of the mechanisms involved and the

forces incurred while lifting are important in the development

of safe lifting techniques. The purpose of this research is

to determine which of the trunk and hip muscles are used when

lifting a crate of 35.25 pounds (for males, 24 pounds for

females), from the floor. I understand that the benefits of

this research will not effect me directly, but the knowledge

gained will have a positive influence upon injury prevention.

In agreeing to participate in this study I understand that I

will be required to lift either a 35.25 (males) pound or a 24

(females) pound crate using a squat lift. A squat lift is one

in which the hips and knees are bent to lower the body down

105

to the object to be lifted. A total of six lifts will be

performed. Three of the lifts with the back in a "bowed-in"

position and three with the back in a "bowed-out" position.

I understand that I will be required to come to Wenner-Gren

Biomechanics laboratory one time and this session will last

approximately one hour. I understand that surface electrodes

and reflective markers will be placed on my body. I also

understand that I will be required to give a maximal exertion

of my abdominal, back extensor and hip extensor muscles.

I understand that participation is voluntary; refusal to

participate will involve no penalty or loss of benefits to

which I am otherwise entitled. I understand that no

compensation is being offered or is available for my

participation.

I understand that I cannot participate in this study if I have

had an episode of low back pain within the last six months or

I have suffered an injury to my knees or hips which interferes

with my ability to squat.

I understand that review of the literature and experience of

the researchers indicate that these weights and procedures are

within the safe and acceptable limits and represent minimal

risk of injury. I understand that there is a chance of

suffering a low back strain secondary to participation.

106

I understand that in the event of physical injury resulting

from this research project in which I am participating, no

form of compensation is available. A physical therapist will

be present at all times during the research project to provide

assistance in the event of an unexpected injury. However, any

medical treatment will be provided at my own expense or at the

expense of my health care insurer. I also understand that if

I desire further information about this matter, I should

contact Jim Vakos, P.T., at 273-5575.

I authorize Jim Vakos and the Department of Health, Physical

Education and Recreation and the Physical Therapy Department

to keep, preserve, use and dispose of the findings from this

research with the provision that my name will not be

associated with any of the results.

I have been given the right to ask, and have answered, any

questions concerning the procedures to be used during this

research. Questions have been answered to my satisfaction.

I understand that my confidentiality and anonymity will be

protected. I further understand that I have the right to

terminate my involvement in this project at any time, without

sustaining any form of penalty. I have read and understand

the contents of this form and received a copy.

107

Subj ect _ _ _ _ _ _ _ _ _ _ _ _ __ Date _ _ _ _ _ _ _ _ _

Witness __ _ _ _ _ _ _ _ _ _ _ _ _ _ Date _ _ _ _ _ _ _ _ _

I have explained and defined in detail the research procedure

in which the subject has consented to participate.

Principle Investigator _____________ Date ____

108

APPENDIX B

109

Medical History Questionnaire

NAME

AGE

SOCIAL SECURITY NUMBER

Answer the following questions by marking the appropriate

response.

1. Have you ever suffered an injury to your low back or an

episode of low back pain?

YES

NO

2. If yes, when did this incident occur?

LESS THAN SIX MONTHS AGO

MORE THAN SIX MONTHS AGO

3. Have you ever suffered an injury to your hips or knees,

or suffer from any condition that would prevent you from

squatting?

YES

NO

4. To the best of your knowledge do you suffer from any

condition that would prevent you from exerting yourself,

i.e. cardiac precautions, emphysema, etc.?

YES

NO

110

BI BLIOGRAPHY

111

Adams, M. A., Hutton, W. C., & Stott, J. R. R. (1980). Theresistance to flexion of the lumbar intervertebral joint.Spine, 5, 245-252.

Andersson, G. B. J. (1985). Loads on the lumbar spine: Invivo measurement and biomechanical analysis. In Winter,D. A. (Ed.), Biomechanics IX-B (pp. 32-35). Champaign,IL: Human Kinetic Publishers.

Andersson, G. B. J. (1981). Epidemiologic aspects of low backpain in industry. Spine, 6, 53-57.

Andersson, G. B. J., Ortengren, R. 0., & Heberts, P. (1977).Quantitative electromyographic studies of back muscleactivity related to posture and loading. OrthopedicClinics of North America, 8, 85-96.

Andersson, G. B. J., Ortengren, R. 0., & Nachemson, A. (1976).Quantitative studies of back loads in lifting. Spine,1, 178-185.

Aspden, R. M. (1989). The spine as an arch: A newmathematical model. Spine, 14, 266-274.

Bartelink, D. L. (1957). The role of abdominal pressure onthe lumbar intervertebral discs. Journal of Bone andJoint Surgery (British ed.), 39, 718-725.

Beiring-Sorensen, F., Thomsen, C. E., & Hilden, J. (1989).Scandinavian Journal of Rehabilitative Medicine, 21, 151-157.

Bigos, S. J., Spengler, D. M., Martin, N. A., Zeh, J., Fisher,L., Nachemson, A., & Wang, M. H. (1986). Back injuriesin industry: A retrospective study, II. Injury factors.Spine, 11, 246-251.

Bogduk, N., & Twomey, L. T. (1987). Clinical anatomy of the

lumbar spine. New York: Churchill Livingstone.

Bogduk, N., & Macintosh, J. E. (1984). The applied anatomyof the thoracolumbar fascia. Seine, 9, 164-170.

Bush-Joseph, C., Schipplein, 0., & Andersson, G. B. J. (1988).Influence of dynamic factors on the lumbar spine momentin lifting. Ergonomics, 31, 211-216.

Carlsoo, S., (1961). The static muscle load in different workpositions: an electromyographic study. Ergonomics, A,193-211.

112

Cook, T. C., & Newman, D. A. (1987). The effect of loadplacement on the emg activity of low back muscles duringload carrying by men and women. Ercionomics, 30, 1413-1423.

Davis, P. R., Troup, J. D. G. & Burnard, J. H. (1965).Movements of the thoracic and lumbar spine when lifting:a chrono-cyclophotgraphic study. Journal of Anatomy -London, 99, 13-26.

Delitto, R. S., Rose, S. J., & Apts, D. W. (1987).Electromyographic analysis of two techniques for squatlifting. Physical Therapy, 67, 1329-1334.

Ekholm, J. Arborelius, U. P., & Nemeuth, G. (1982). The loadon the lumbo-sacral joint and trunk muscle activityduring lifting. Ergonomics, 25, 145-161.

Freivalds, A., Chaffin, D. B., Garg, A., & Lee, K. S. (1984).A dynamical biomechanical evaluation of lifting, maximumacceptable loads. Journal of Biomechanics, 17, 251-262.

Gagnon, M. Sicard, C., & Drouin, G. (1985). Evaluation ofloads on the lumbar spine with motion analysis techniquesand a static plana model. In Winter, D. A. (Ed.),Biomechanics IX-B (pp. 44-49). Champaign, IL: HumanKinetic Publishers.

Gracovetsky, S. (1988). The Spinal Engine. New York, NY:Springer-Verlag

Gracovetsky, S., Farfan, H. & Hueller, C. (1985). Theabdominal mechanism. Spine, 10, 317-324.

Gracovetsky, S., Farfan, H. F., & Lamy, C. (1981). Themechanism of the lumbar spine. Spine, 6, 249-261.

Hart, D. L., Stobbe, T. J., & Jaraeid, M. (1987). Effect oflumbar posture on lifting. Spine, 12, 138-145.

Hemborg, B., Moritz, U., Hemborg, J., Lowing, H., & Akesson,I. (1983). Intra-abdominal pressure and trunk muscleactivity during lifting and effect of abdominal trainingon healthy subjects. Scandinavian Journal ofRehabilitative Medicine, 15, 183-196.

Jonsson, B. (1985) The value of electromyographic measures inthe assessment of muscular load and fatigue in work placetasks. In Winter, D. A. (Ed.), Biomechanics IX-B (pp.3-5). Champaign, IL: Human Kinetic Publishers.

113

Joseph, J., & Williams, P. L. (1957). Electromyography ofcertain hip muscles. Journal of Anatomy, 91, 286-294.

Kippers, V., & Parker, A. W. (1984). Posture related tomyoelectric silence of erector spinae during trunkflexion. Spine, 9, 740-745.

Lin, H. S., Liu, Y. K., & Adams, K. H. (1978). Mechanicalresponse of the lumbar intervertebral joint underphysiological (complex) loading. Journal of Bone andJoint Surgery, 60-A, 41-55.

Lindh, M. (1989) Biomechanics of the lumbar spine. InNordin, M., & Frankel, V. H. (ed). Basic biomechanicsof the musculoskeletal system (2w ed.). Philadelphia:Lea and Febiger

McGill, S. M., & Sharratt, M. T. (1990). Relationship betweenintra-abdominal pressure and trunk EMG. ClinicalBiomechanics, 5, 59-67.

McGill, S. M., & Norman, R. W. (1987). Reassessment of therole of intra-abdominal pressure in spinal compression.ErQonomics, 30, 1565-1588.

McGill, S. M., & Norman, R. W. (1986). Partitioning of theL4-L5 dynamic moment into disc, ligamentous and muscularcomponents during lifting. Sine, 11, 666-678.

McGill, S. M., & Norman, R. W. (1985). Dynamically andstatically determined low back movement during lifting.Journal of Biomechanics, 18, 877-885.

Macintosh, J. E., & , N. (1987). The biomechanics of thethoracolumbar fascia. Clinical Biomechanics, 2, 78-83.

Ortengren, R., Andersson, G. B. J., & Nachmeson, A. L. (1981).Studies of relationships between lumbar disc pressure,myoelectric back muscle activity and intra-abdominal(intragastric) pressure. Spine, 6, 98-103.

Panjabi, M. H., Tech, D., & White, A. (1980). Basicbiomechanics of the spine. NeurosurQery, 2, 76-93.

Portnoy, H., & Morin, F. (1958). Electromyographic study ofpostural muscles in various positions and movements.American Journal of Physiology, 186, 122-126.

. . . . ... . z . . ..

114

Seroussi, R. E., & Pope, M. E. (1987). The relationshipbetween trunk muscle electromyography and lifting momentsin the sagittal and frontal planes. Journal ofBiomechanics, 20, 135-146.

Sihvonen, T., Partanen, J. & Hanninen, 0. (1988). Averaged(rms) surface emg in testing back function.Electromyography Clinics in Neurophysiology, 28, 335-339.

Spengler, D. M., Bigos, S. J., Martin, N. A., Zeh, J., Fisher,L. & Nachemson, A. (1986). Back injuries in industry:A retrospective study. Overview and cost analysis.Spine, i1, 241-245.

Sullivan, M. S. (1989). Back support mechanisms during manuallifting. Physical Therapy, 69, 38-46.

Tanii, K., & Masuda, T. (1985). A study by EMG stick diagramsof the muscular activities in the trunk flexion andextension movement. ErQonomics, 28, 895-904.

Troup, J. D. G. (1977). Dynamic factors in the analysis ofstoop and crouch lifting methods: A methodologicalapproach to the development of safe materials handlingstandards. Orthopedic Clinics of North America, 8, 201-209.

Zetterberg, C., Andersson, G. B. J., & Schultz, A. B. (1987).The activity of individual trunk muscles during heavyphysical loading. Spine, i0, 1035-1040.

115

VITA

Education: University of Wisconsin-Parkside.Salem, WisconsinB.S. degree, Chemistry, 1974

Marquette UniversityMilwaukee, WisconsinB.S. degree, Physical Therapy, 1978

University of KentuckyLexington, KentuckyM.S. Physical Education, 1990

Professional: Staff Physical TherapistN. Chicago Veterans Medical CenterSeptember 1978 - February 1983

Staff Physical TherapistUnited States Air ForceMarch 1983 - Present

(Author's Name)

(Date)